Many venous access devices (VADs) are routinely flushed with small doses of heparinized saline (2 to 3 cc, 100 units/cc). In larger intravenous doses, heparin causes immune-mediated thrombocytopenia in 1 to 3 percent of patients and leads to heparin-related antibodies in approximately 5 to 50 percent of patients. The risk of heparin-induced thrombocytopenia from daily VAS flushed, as reflected in the appearance of heparin-related antibodies, is not known. The purpose of this study is to estimate this risk by testing for heparin-induced antibodies in serum samples.Presence of heparin-induced antibodies will be evaluated in 120 subjects before VAD insertion and approximately 4 and 8 weeks later. The protocol was amended to include catheters in place for less than 24 hours. To date, 47 subjects have been enrolled.